The various purposes for which a dynamic tasks might be constructed, such as to test for knowledge, teach, or to assist professionals or the lay public in understanding the systems they are dealing with (or part of), are discussed. The idea analysis method is suggested as a means to fit a task to its purpose. Idea analysis entails analysing the task in terms of what basic ideas need to be familiar if one is to be able solve the task. It is just as important to know what knowledge a task does not require as to know what it does require, and if the requirements corresponds to the goal(s) motivating the construction of the task. To provide an example, the Computer Security Incident Response Team (CSIRT) task, a close analogue to the one-stock reindeer management task by Moxnes, is analysed, and several issues of general importance are revealed.